Mobile communication terminal apparatus

ABSTRACT

A mobile communication terminal apparatus which performs radio communication with base stations using an adaptive array antenna which obtains an antenna output by multiplying output signals from the respective antenna elements of an array antenna by weighting factors using multipliers, and adding the resultant data using an adder estimates the arrival direction of radio waves from the base station, and starts adaptive control on the adaptive array antenna, at the time of handover from the one base station to the other base station, by using as initial values the weighting factors obtained in accordance with the arrival direction estimation result obtained prior to the handover.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based upon and claims the benefit of priorityfrom the prior Japanese Patent Application No. 2000-393202, filed Dec.25, 2000, the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a mobile terminal apparatus forperforming radio communication with a base station and, moreparticularly, to a mobile communication terminal apparatus using anadaptive array antenna.

[0004] 2. Description of the Related Art

[0005] An adaptive array antenna is an antenna which weights outputsfrom a plurality of antenna elements comprising an array antenna andarrayed in a predetermined shape by multiplying the outputs by weightingfactors and can adaptively change directivity by controlling theweighting factors. Recently, a radio communication system with mobilecommunication terminals equipped with such adaptive array antennas hasbeen under research and development.

[0006]FIG. 16 shows a typical example of a radio communication systemusing such mobile communication terminals. A mobile terminal 1000adaptively controls weighting factors for a mounted adaptive arrayantenna 1010 to synthesize a beam pattern 1011 whose directivity is settoward a base station 1001 for the other party, thereby communicatingwith the base station 1001. This makes it possible to suppresstransmission power and reduce power consumption as compared with a casewhere each mobile terminal is equipped with an omnidirectional antenna.When, therefore, this mobile terminal uses a power supply with a limitedcapacity, e.g., a battery, it can perform communication for a longerperiod of time. In addition, since radiation of interference power inother directions can be suppressed, interference with base stationsother than the base station 1001 in communication can be suppressed.

[0007] In such a radio communication system, handover is performed whenreception electric field strength necessary for the continuation ofcommunication cannot be obtained as the mobile terminal 1000 graduallymoves away from the base station 1001 for the other party. At the timeof handover, it is required to synthesize a new beam pattern 1012 whosedirectivity is set toward a base station 1002 to which the mobileterminal 1000 is located close upon movement. To newly synthesize a beampattern for the adaptive array antenna, a signal processing time isrequired for adaptive control on weighting factors. As a consequence,communication is interrupted for the signal processing time required foradaptive control accompanying the change from the beam pattern 1011 tothe beam pattern 1012.

[0008] As described above, in a mobile communication terminal equippedwith a conventional adaptive array antenna whose directivitycharacteristics can be adaptively changed, a signal processing time isrequired to adaptively control weighting factors for directivitysynthesis for the adaptive array antenna. For this reason, communicationis interrupted during the signal processing time required for adaptivecontrol accompanying a change in beam pattern at the time of handover.

BRIEF SUMMARY OF THE INVENTION

[0009] The present invention has been made to solve the above problems,and has as its object to provide a mobile communication terminalapparatus using an adaptive array antenna which can realize handover athigh speed.

[0010] According to the embodiment of the present invention, there isprovided a mobile communication terminal apparatus which communicateswith either a first base station or a second base station and performs ahandover from one to another of the base stations. The mobilecommunication terminal apparatus comprises: an array antenna whichoutputs a plurality of signals; a plurality of multipliers that multiplythe signals output from the array antenna by weighting factors, andoutput multiplication result signals; a reception device configured togenerate a reception signal based on the multiplication result signalsoutput from the multipliers; a control device configured to perform acalculation for the weighting factors based on the reception signal, andadaptively control the multipliers by supplying the calculated weightingfactors thereto; and an initial value calculating device configured tocalculate at least one initial value for the weighting factors prior tothe handover. In this apparatus, the control device starts thecalculation for the weighting factors using the initial value when thehandover is performed.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0011]FIG. 1 is a view for explaining an outline of a radiocommunication system including a mobile terminal apparatus according tothe first embodiment of the present invention;

[0012]FIG. 2 is a block diagram showing the arrangement of a transceiverin the mobile terminal apparatus according to the first embodiment;

[0013]FIG. 3 is a block diagram showing the arrangement of a controlcircuit in the first embodiment;

[0014]FIG. 4 is a view for explaining an arrival direction/weightingfactor storage section in the first embodiment;

[0015]FIG. 5 is a flow chart showing the main flow of processing in thefirst embodiment;

[0016]FIG. 6 illustrates an example of the internal structure of theweighting factor calculating section 304 shown in FIG. 3;

[0017]FIG. 7 is a block diagram showing another arrangement of a controlcircuit in the first embodiment;

[0018]FIG. 8 is a block diagram showing still another arrangement of acontrol circuit in the first embodiment;

[0019]FIG. 9 is a view for explaining an outline of a radiocommunication system including a mobile terminal apparatus according tothe second embodiment of the present invention;

[0020]FIG. 10 is a block diagram showing the arrangement of atransceiver in the mobile terminal apparatus according to the secondembodiment;

[0021]FIG. 11 is a flow chart showing the main flow of processing in thesecond embodiment;

[0022]FIG. 12 is a part of a flow chart showing the flow of processingfor base station list update in the second embodiment;

[0023]FIG. 13 is a view for explaining a base station list;

[0024]FIG. 14 is another part of a flow chart showing the flow ofprocessing for base station list update in the second embodiment;

[0025]FIG. 15 is another part of a flow chart showing the modified flowof processing for base station list update in the second embodiment; and

[0026]FIG. 16 is a view for explaining an outline of a radiocommunication system including conventional mobile communicationterminal apparatuses.

DETAILED DESCRIPTION OF THE INVENTION

[0027] The embodiments of the present invention will be described belowwith reference to the accompanying drawing.

First Embodiment

[0028]FIG. 1 is a view for explaining an outline of a radiocommunication system according to the first embodiment of the presentinvention. FIG. 1 shows a state where a mobile communication terminalapparatus (to be simply referred to as a mobile terminal hereinafter)100 such as a portable telephone, portable radio unit, or portableinformation terminal having an adaptive array antenna is communicatingwith a base station 101 by the TDMA (Time Division Multiple Access)communication scheme.

[0029] In the TDMA communication scheme, as indicated by the upper sideof FIG. 1, a communication channel is divided into a plurality of frames(TDM frames), and each TDM frame is divided into a plurality of timeslots S1, S2, and S3. When the mobile terminal 100 is to performcommunication, one time slot is generally assigned to it per frame.

[0030] In the case shown in FIG. 1, time slot S1 is assigned forcommunication from the base station 101 to the mobile terminal 100. Intime slot S1 in each TDM frame, the mobile terminal 100 receives atransmission signal from the base station 101 by using an antenna beam111 combined by an array antenna 110. In other time slots S2 and S3, thebase station 101 outputs no transmission signal to the mobile terminal100.

[0031] The mobile terminal 100 estimates the arrival direction of radiowaves from a neighboring base station 102 other than the base station101, with which the mobile terminal is currently communicating, by usingthe time zones of time slots S2 and S3 other than time slot S1 used forreception or a predetermined period of time taken for antenna beamswitching, e.g., a time zone except for portions near the beginning oftime slot S2 and the end of time slot S3. If the mobile terminal 100 isnot moving at high speed, there is no need to estimate arrivaldirections in all the time zones of time slots S2 and S3. However, inconsideration of at least the moving speed of the mobile terminal 100,arrival direction estimation is performed at time intervals at whicharrival direction estimation results do not extremely vary. A specificexample of this arrival direction estimation will be described in detaillater.

[0032] The mobile terminal 100 calculates a weighting factor fordirecting an antenna beam to an estimated arrival direction orcalculates a weighting factor for null-steering the base station 101that is currently performing communication by using time slot S1 andstores it in a memory, together with, for example, an arrival directionestimation result and reception level information. In performinghandover from the base station 101 to the base station 102, the arrivaldirection estimation result and weighting factor that have beencalculated and stored in the memory are used as initial values, andadaptive control on the adaptive array antenna is started.

[0033] With this operation, even if communication is abruptlyinterrupted as the mobile terminal 600 separates from the base station601 in communication or an obstacle such as a building comes between theterminal an the base station 601, the mobile terminal 100 can makeadaptive control on the adaptive array antenna quickly converge, thussolving the conventional problems. This operation will be described inmore detail below.

[0034]FIG. 2 shows an example of the arrangement of a transceiver usedin the mobile terminal 100 according to this embodiment. The arrayantenna 110 shown in FIG. 1 is used. This antenna is formed by arrayinga plurality of antenna elements A1, A2, A3, and A4 in a predeterminedshape, e.g., a linear or circular shape. Unnecessary components areremoved from an output signal from each of the antenna elements of thearray antenna 110 by a filter (e.g., bandpass filter) 201. The resultantsignal is amplified by a low-noise amplifier (LNA) 202 and input to amixer 203. This signal is then multiplied by a local signal suppliedfrom a local oscillator 204 through a distributor 205 to befrequency-converted (downconverted). A filter 206 removes unnecessarycomponents from the output from the mixer 203. The resultant signal isdemodulated by a quadrature demodulator 207 and converted into a digitalsignal by an A/D converter (ADC) 208. The bandpass filters 201, LNAs202, mixers 203, local oscillators 204, distributors 205, filters 206,quadrature demodulators 207, and A/D converters 208 are equal in numberto the antenna elements of the array antenna 110.

[0035] The digital signals output from the A/D converters 208 are inputto a digital signal processing section (DSP) 210. In the digital signalprocessing section 210, the digital signals from the A/D converters 208are input to multipliers (complex multipliers) 211 to be multiplied byweighting factors (complex weighting factors) concerning amplitude andphase. The outputs from the multipliers 211 are added by an adder 212.The output from the adder 212 is detected by a detection circuit 213.The output from the detection circuit 213 is supplied as a receptionsignal to the subsequent circuit (not shown) and also input to a controlcircuit 214. The digital signals from the A/D converters 208 have alsobeen input to the control circuit 214. The control circuit 214 suppliesweighting factors to the multipliers 211. The control circuit 214 willbe described in detail later.

[0036] In addition to a master synchronization circuit 215 used fortransmission/reception to/from the base station 101 that is currentlycommunicating with the mobile terminal 100, the digital signalprocessing section 210 includes a slave synchronization circuit 216 usedfor transmission/reception to/from at least one base station (e.g., thebase station 102 in FIG. 1) other than the base station 101. Thesesynchronization circuit 215 and 216 are circuits for performing bitsynchronization and frame synchronization and formed by using, forexample, PLLs (Phase Locked Loops). The synchronization circuits 215 and216 are switched by using switches 217 and 218.

[0037] When the mobile terminal 100 is to communicate with the basestation 101, the switches 217 and 218 are connected to the sidesindicated by the solid lines. In this state, the output from the adder212 is input to the master synchronization circuit 215 through theswitch 217, and the output from the master synchronization circuit 215is input to the detection circuit 213 and control circuit 214 throughthe switch 218. Likewise, when the mobile terminal 100 is to communicatewith the base station 102, the switches 217 and 218 are connected to thesides indicated by the dashed lines. In this state, the output from theadder 212 is input to the slave synchronization circuit 216 through theswitch 217, and the output from the slave synchronization circuit 216 isinput to the detection circuit 213 and control circuit 214 through theswitch 218. The signals supplied from the synchronization circuits 215and 216 to the detection circuit 213 are reference signals forsynchronous detection, and clock signals synchronized with thesereference signals are input to the control circuit 214.

[0038] As described above, in the mobile terminal 100, the slavesynchronization circuit 216 used to receive a transmission signal fromanother base station 102 is prepared in addition to the mastersynchronization circuit 215 used to receive a transmission signal fromthe base station 101 in communication. This makes it possible to obtainexcellent error rate characteristics by synchronous detection evenduring intermittent transmission/reception of signals to/from the basestation 102. In addition, this allows the control circuit 214 to easilyapply a necessary direction estimation algorithm to a signal afterdetection by the detection circuit 213.

[0039] Furthermore, the mobile terminal 100 receives a signal from thebase station 102 other than the base station 101 in a burst form, i.e.,intermittently. For this reason, the PLL time constant used for theslave synchronization circuit 216 during a reception period is made todiffer from that during a non-reception period. During a non-receptionperiod, the time constant is increased so as not to change a parametermuch to suppress variations in phase. This makes it possible to keep asynchronous state even during the non-reception period, and allowssynchronous detection from different base stations.

[0040] The control circuit 214 will be described next with reference toFIG. 3.

[0041]FIG. 3 shows the arrangement of a portion of the control circuit214 which is associated with weighting factor control. This portionincludes an arrival direction estimating section 303, weighting factorcalculating section 304, and weighting factor storage section 305 inaddition to a main weighting factor calculating section 301 andweighting factor holding section 302. The main weighting factorcalculating section 301 calculates optimal weighting factors on thebasis of the digital signals output from the A/D converters 208 and thereception signal from the detection circuit 213 in FIG. 3. Thisweighting factor calculation is performed on the principle ofminimizing, for example, the error signal between a reception signal anda reference signal. The weighting factors calculated by the mainweighting factor calculating section 301 are supplied to the multipliers211 through the weighting factor holding section 302 for holding theweighting factors up to the next frame.

[0042] The arrival direction estimating section 303 estimates thearrival direction of radio waves from the base station 102 or the like(to be represented by the base station 102) other than the base station101 with which the mobile terminal 100 is currently communicating.Examples of this estimation method are:

[0043] (1) A “beam scan”, i.e., scanning around the mobile terminal 100by changing the maximum directivity direction of the adaptive arrayantenna, is performed to detect a direction in which the maximumreception electric field strength is obtained, and the detecteddirection is estimated as the arrival direction of radio waves. Morespecifically, the level of a reception signal from the detection circuit213 is monitored while a beam scan is performed by sequentially changingweighting factors, and a direction corresponding to weighting factorswith which the maximum reception signal level is obtained is estimatedas an arrival direction.

[0044] (2) A “null scan”, i.e., scanning around the mobile terminal 100by changing the null direction corresponding to a valley of theradiation determined of the adaptive array antenna to detect a directionin which the minimum reception electric field strength is obtained, andthis direction is estimated as the arrival direction of radio waves. Toimplement this method, the level of a reception signal from thedetection circuit 213 may be monitored while a null scan is performed bysequentially changing weighting factors, and a direction correspondingto weighting factors with which the minimum reception signal level isobtained may be estimated as an arrival direction.

[0045] (3) Direction estimation may be performed by using, for example,a method based on eigenvalue development such as MUSIC (Multiple SignalClassification) or ESPRIT (Estimation of Signal Parameters viaRotational Invariance Techniques) known as a high-resolution arrivaldirection estimation algorithm, or root MUSIC or unitary ESPRIT whichare modifications of these methods. Although these methods requirelarger signal processing amounts for estimation, the estimationprecision is high.

[0046] If the arrival direction of radio waves from the base station 102is successfully estimated by the arrival direction estimating section303, weighting factors for directing an antenna beam toward the arrivaldirection are calculated by the weighting factor calculating section304. The weighting factors calculated in this manner are stored in theweighting factor storage section 305 in a table form like that shown inFIG. 4 in correspondence with the arrival direction and reception level.In some cases, there are a plurality of neighboring base stations 102other than the base station 101 in communication. Therefore, weightingfactors corresponding to the arrival directions of radio waves from therespective base stations are stored in correspondence with the arrivaldirections and reception levels. “Reception level” indicates the levelof a reception signal output from the detection circuit 213. Note thatsince the arrival directions and weighting factors in the table shown inFIG. 4 exhibit a one-to-one correspondence, the information aboutarrival directions may be omitted.

[0047] When the mobile terminal 100 needs to perform handover, weightingfactors corresponding to the maximum reception level are read out fromthe weighting factor storage section 305. The main weighting factorcalculating section 301 receives the weighting factors read out from theweighting factor storage section 305 as initial values, and startscalculating (updating) weighting factors from the initial values, i.e.,adaptive control on the optimal weighting factors for communication withthe base station 102.

[0048] The flow of processing in this embodiment will be described nextwith reference to the flow chart of FIG. 5.

[0049] First of all, the base station 101 assigns time slot Sn (e.g.,Sn=S1) used for communication with the mobile terminal 100 (S501). Whentime slot Si is then set to Sn, and time slot Sn starts, the mobileterminal 100 directs an antenna beam to the base station 101, receives atransmission signal from the base station 101 by using time slot Sn, andcontinues this reception until the end of time slot Sn (S502 to S504).It is checked at the end of time slot Sn whether the communication is tobe continued (S505). If it is determined that the communication is notcontinued, termination processing is performed (S506). If it isdetermined that the communication is to be continued, it is checkedwhether a predetermined period of time or more has elapsed from theprevious arrival direction estimation (S507).

[0050] If it is determined in step S507 that the predetermined period oftime has not elapsed at the end of time slot Sn, the flow returns tostep S502. If it is determined that the predetermined period of time haselapsed, the arrival direction estimating section 303 estimates thearrival direction of radio waves from the base station 102 other thanthe base station 101 which is currently communicating with the mobileterminal 100 (S508). The weighting factor calculating section 304calculates weighting factors on the basis of the estimated arrivaldirection (S509). The estimated arrival direction, the reception level,and the calculated weighting factors are then stored in the weightingfactor storage section 305 in correspondence with each other (S510).

[0051] If it is determined in step S511 that the mobile terminal 100needs to perform handover while communicating with the base station 101,i.e., the mobile terminal 100 needs to shift to communication with thebase station 102 while communicating with the base station 101, theweighting factors corresponding to the arrival direction of radio wavesfrom the base station 102, which are stored in the weighting factorstorage section 305, are supplied as initial values to the mainweighting factor calculating section 301 to start adaptive control onweighting factors for the reception of radio waves from the base station102 (S512).

[0052] Assume that there are a plurality of base stations 102 around thebase station 101. In this case, since weighting factors corresponding tothe arrival directions of radio waves from these base stations 102 arestored in the weighting factor storage section 305, together with thearrival directions and reception levels, weighting factors correspondingto one of these base stations which exhibits the highest reception levelare supplied as initial values to the main weighting factor calculatingsection 301 in step S512, thereby starting adaptive control on weightingfactors for the reception of radio waves from the base stationexhibiting the highest reception level.

[0053] If it is determined in step S513 that handover from the basestation 101 to the base station 102 has failed, termination processingis performed (S514). If the handover has succeeded, the base station 102assigns time slot Sm (S515), and Si is set to Sm to repeat theprocessing after step S502.

[0054] As described above, according to this embodiment, when the mobileterminal 100 is to perform handover from the base station 101 to thebase station 102, weighting factors calculated in advance in accordancewith the arrival direction of radio waves from the base station 102 aresupplied as initial values from the weighting factor storage section 305to the weighting factor calculating section 301, thus making adaptivecontrol on weighting factors quickly converge.

[0055] Alternatives of the present embodiment are explained below.

[0056]FIG. 6 illustrates an example of the internal structure of theweighting factor calculating section 304 shown in FIG. 3.

[0057] In this detailed example, a weighting factor initial valuecalculating section 1401 which calculate the value directed from anestimated arrival direction, has a function similar to that of theweighting factor calculating section 304. The calculating section 1401calculates a weighting factor with which the maximum directivity can bedirected in an estimated arrival direction on the basis of the arrivaldirection estimation result from the arrival direction estimatingsection 303, and then outputs the calculated result as an initial value.The weighting factor updating section 1402 handles this initial value asan initial value for the weighting factor for an array antenna used forreceiving a signal from a corresponding base station other than thosebeing engaged in communications. The weighting factor updating section1402 also receives an ADC output received via each antenna element. Theupdating section 1402 applies an adaptive control algorithm such as LMS(Least Mean Square) to the initial value, and thus the weighting factoris updated. With this structure, such an advantage that the convergingtime can be shortened as compared to the case where a direct output fromthe calculating section 1401 is given as the initial value to the mainweighting calculating circuit 301 at the time of handover.

[0058] It should be noted that in the above remodeled version, thearrival directions and weighting factors do not exhibit a one-to-onecorrespondence with respect to the table shown in FIG. 4.

[0059] Another version proposes a structure such as shown in FIG. 6, inwhich an initial value output control circuit 1403 which is incompliance with the signal reception level is provided. In this version,only when the received signal level is detected to be larger than apredetermined threshold value on the basis of the data regarding thereceived signal level outputted from the detector circuit 213, it isdetermined that the error of the estimated result of the arrivaldirection is small, and accordingly the initial value is outputted fromthe weighting factor initial value calculating section 1401.

[0060] Next, other examples of the controller circuit shown in FIG. 3are explained bellow.

[0061]FIG. 7 shows a case where only the estimation of an arrivaldirection to other base station is carried out, and the table of a basestation is designed to store estimated arrival directions and receivedsignal levels when they arrive. The advantage of this structure is thatthe size of the base station table can be reduced. Further, thestructure is not designed to calculate the initial value of theweighting factor for each case, and therefore the resources of hardwareand software can be assigned diversely to the estimation process for thearrival direction. This structure is particularly suitable for the caseof estimating a high resolution arrival direction, which requires a lotof processing time, which is employed in place of the directionestimation by beam scan, which does not usually require such a long timefor processing but entails a slightly low accuracy. With this structure,it is possible to improve the direction estimation accuracy.

[0062]FIG. 8 illustrates the structure of a case where an arrivaldirection estimation unit is not provided but a second weighting factorcalculating circuit is provided. This structure is particularly suitablefor the case where the weighting factor to other base station than thebase station which is being in communication, can be calculated at anaccuracy of some degree without estimating the arrival direction, whilereceiving signals at a timing other than that of the communication slotwith the base station in communications.

[0063] Examples of the above case are: the case where there are not manybase stations transmitting signals at a timing other than that of thecommunication slot with the base station being engaged incommunications, and the interference is not severe, due to the fact, forexample, that the base stations are not densely located, and the casewhere a secondary modulation (or primary modulation) is carried out on asignal such as another kind of diffusion symbol, and therefore thesignals from the base station is less likely to be interfered with afterreverse diffusion of the secondary modulation.

[0064] It should be noted that the advantage of the structure shown inFIG. 3 is that the initial value of weighting on each antenna element isalready calculated at the time of handover, and therefore thecalculation amount in the handover is less as compared to the structureshown in FIG. 7. Further, the advantage of the structure shown in FIG. 3(and FIG. 6) which includes an arrival direction estimating unit is thatthe estimation result of the arrival direction can be used for theinitial value of the weighting calculating circuit, and therefore theconversing speed of the repetitious calculations for the weightingfactor for the antenna is improved as compared to the case shown in FIG.8.

Second Embodiment

[0065] The second embodiment of the present invention will be describednext. FIG. 9 is a view for explaining an outline of a radiocommunication system according to the second embodiment. Like FIG. 1,FIG. 9 shows a state where a mobile communication terminal apparatus (tobe simply referred to as a mobile terminal hereinafter) 600 equippedwith an adaptive array antenna, such as a portable telephone, portableradio unit, or portable information terminal is communicating with abase station 601 by the CDMA (Code Division Multiple Access)communication scheme.

[0066] According to the CDMA communication scheme, as indicated by theupper side of FIG. 9, communication channels are multiplexed by aplurality of types of spreading codes C1, C2, and C3. The mobileterminal 600 has, for example, two reception circuits including beamcombining/despreading circuits and is designed to form antenna beams 611and 612 by using the respective reception circuits. In the case shown inFIG. 9, the mobile terminal 600 receives a transmission signal from thebase station 601, which uses the spreading code C1, by using the antennabeam 611 formed by one of the reception circuits.

[0067] The mobile terminal 600 also estimates the arrival direction ofradio waves which use the spreading code C2 and are sent from theneighboring base station 602 other than the base station 601 incommunication by, for example, scanning around the terminal bydeflecting the antenna beam 612 formed by the other reception circuit orperforming signal processing for an input signal vector to the adaptivearray antenna. In this case, in consideration of the moving speed of themobile terminal 600, arrival direction estimation is performed at timeintervals at which arrival direction estimation results do not extremelyvary.

[0068] Subsequently, the mobile terminal 600 calculates weightingfactors for directing an antenna beam toward the estimated arrivaldirection in accordance with the arrival direction estimation result, asin the first embodiment, or weighting factors that can null-steer thebase station 601 in communication, and stores them in the memory,together with the arrival direction estimation result. In performinghandover from the base station 601 to the base station 602, the arrivaldirection estimation result and weighting factors calculated and storedso far are supplied as initial values, thereby starting adaptive controlon the adaptive array antenna.

[0069] With this operation, even if communication is abruptlyinterrupted as the mobile terminal 600 separates from the base station601 in communication or an obstacle such as a building comes between theterminal an the base station 601, divergence of adaptive control on theadaptive array antenna can be quickened.

[0070]FIG. 10 shows an example of the arrangement of a transceiver usedin the mobile terminal 600 in this embodiment. An antenna array 610,filters 701, LNAs 702, mixers 703, local oscillator 704, distributor705, filters 706, quadrature demodulators 707, and A/D converters (ADCs)708 have the same arrangements as those in the mobile terminal 100 inFIG. 2 according to the first embodiment.

[0071] A digital signal processing section (DSP) 709, to which thedigital signals output from the A/D converters 708 are input, has tworeception circuits 710 and 720. When the mobile terminal 600 receives atransmission signal from the base station 601 with which the terminal iscurrently communicating, one reception circuit 710 is used. In receivinga transmission signal from another base station 602, the other receptioncircuit 720 is used.

[0072] The digital signals input to the reception circuits 710 an 720 inthe digital signal processing section 709 are input a plurality of firstmultipliers 711 and a plurality of second multipliers 721, which arecomplex multipliers, to be multiplied by weighting factors (complexweighting factors) associated with amplitude and phase. Outputs from themultipliers 711 and 721 are added by adders 712 and 722, respectively.Outputs from the adders 712 and 722 are despread by despreading circuits713 and 723 using spreading codes and detected by detection circuits 714and 724. Outputs from the detection circuits 714 and 724 are supplied asreception signals to the subsequent circuits (not shown) and also inputto control circuits 715 and 725. The control circuits 715 and 725 thensupplies weighting factors to the multipliers 711 and 721. The basicarrangement of each of the control circuits 715 and 725 is the same athat of the control circuit 214 in FIG. 2 in the first embodiment.

[0073] The reception circuits 710 and 720 also have synchronizationcircuits 716 and 726, respectively. The synchronization circuits 716 and726 are circuits for performing bit synchronization and framesynchronization when the mobile terminal 600 performstransmission/reception of signals to/from the base stations 601 and 602,i.e., the reception circuits 710 and 720 receive transmission signalsfrom the base stations 601 and 602. For example, these synchronizationcircuits are formed by using PLLs. The synchronization circuits 716 and726 respectively supply spreading codes (e.g., C1 and C2) to thedespreading circuits 713 and 723, reference signals for synchronousdetection to the detection circuits 714 and 724, and clock signals tothe control circuits 715 and 725.

[0074] By providing the synchronization circuits 716 and 726 for the tworeception circuits 710 and 720 in the mobile terminal 600, respectively,excellent error rate characteristics based on synchronous detection canbe obtained even in intermittent transmission/reception of signalsto/from the base station 602. In addition, this allows the controlcircuits 715 and 725 to easily apply a necessary direction estimationalgorithm to signals after detection by the detection circuits 714 and724.

[0075] Furthermore, the mobile terminal 600 receives a signal from thebase station 602 other than the base station 601 in a burst form, i.e.,intermittently. For this reason, the PLL time constant used for thesynchronization circuit 726 during a reception period is made to differfrom that during a non-reception period. During a non-reception period,the time constant is increased so as not to change a parameter much tosuppress variations in phase. This makes it possible to keep asynchronous state even during the non-reception period, and allowssynchronous detection from different base stations.

[0076] The flow of processing in this embodiment will be described nextwith reference to the flow chart of FIG. 11.

[0077] First of all, a spreading code Cn (e.g., Cn=C1) to be used forcommunication with the base station 601 with which the mobile terminal600 communicates first is determined (S801). A spreading code Ci is thenset to Cn, and the mobile terminal 600 directs an antenna beam to thebase station 601 and receives a transmission signal from the basestation 601 by using the spreading code Cn (S802). In step S803, it ischecked whether the communication is continued. If the communication isnot continued, termination processing is performed (S804). If thecommunication is continued, it is checked whether a predetermined periodof time has elapsed since the previous arrival direction estimation(S805).

[0078] If it is determined in step S805 that the predetermined period oftime has not elapsed from the previous arrival direction estimation, theflow returns to step S802. If the predetermined period of time haselapsed, the arrival direction estimating section in the control circuit725 estimates the arrival direction of radio waves from the base station602 other than the base station 601 with which the mobile terminal 600is currently communicating (S806). The weighting factor calculatingsection in the control circuit 725 then calculates weighting factor onthe basis of the estimated arrival direction (S807). The calculatedweighting factors are stored in the weighting factor storage section inthe control circuit 725 in correspondence with the estimated arrivaldirection and reception level (S808).

[0079] If it is determined in step S809 that the mobile terminal 600needs to perform handover while communicating with the base station 601,i.e., the mobile terminal 600 needs to shift to communication with thebase station 602 while communicating with the base station 601, theweighting factors corresponding to the arrival direction of radio wavesfrom the base station 602, which are stored in the weighting factorstorage section in the control circuit 725, are supplied as initialvalues to the weighting factor calculating section in the controlcircuit 725 to start adaptive control on weighting factors for thereception of radio waves from the base station 602 (S810).

[0080] Assume that there are a plurality of base stations 602 around thebase station 601. In this case, since weighting factors corresponding tothe arrival direction of radio waves from the base stations 602 arestored in the weighting factor storage section in the control circuit725, together with the arrival direction and reception level, weightingfactors corresponding to one of the base stations which exhibits thehighest reception level are supplied as initial values to the weightingfactor calculating section in the control circuit 725, thereby startingadaptive control on weighting factors for the reception of radio wavesfrom the base station exhibiting the highest reception level in stepS810.

[0081] If it is determined in step S811 that handover from the basestation 601 to the base station 602 has failed, termination processingis performed (S812). If the handover has succeeded, the base station 602and a spreading code Cm are determined (S813), and Ci is set to Cm torepeat the processing after step S802.

[0082] As described above, in this embodiment as well, when the mobileterminal 600 is to perform handover from the base station 601 to thebase station 602, weighting factors calculated in advance in accordancewith the arrival direction of radio waves from the base station 602 aresupplied as initial values, thus making adaptive control on weightingfactors quickly converge.

[0083] In addition, this embodiment may also perform handover processingbased on a base station list indicating the following link assignmentpriorities. As shown in FIG. 12, the mobile terminal 600 recognizes theidentification information (base station ID) of the base station 602(arrival direction estimation target) other than the base station 601with which the terminal is currently communicating from the spreadingcode multiplexed with a signal on a specific channel such as a pilotchannel transmitted from the base station 602 (S901). The mobileterminal 600 then transmits the reception intensity information of radiowaves transmitted from the base station 602, e.g., a PSMM (PilotStrength Measurement Message), to the base station 601 or a controlstation (MSC), together with the base station ID of the base station 602(S902). The base station 601 or MSC, which has received this PSMM, thenupdates the contents of the base station list managed by the station(S903). The PSMM is obtained by the mobile terminal 600 from thereception signal level of a signal on a pilot channel transmitted fromthe base station 602.

[0084] The base station list is a list which indicates a relationshiprepresenting the transmission/reception states between the respectivemobile terminals and the respective base stations so as to representlink assignment priorities. For example, as shown in FIG. 13, this listis expressed in the form of a table in which the pieces ofidentification information (terminal IDs) of the respective mobileterminals and the respective base station IDs are made to correspond toeach other with relationship parameters of three levels corresponding toPSMMs, namely Active set, Candidate set, and Neighbor set. Referring toFIG. 13, the terminal IDs are expressed by uppercase letters, and thebase stations ID are expressed by lowercase letters. Active setcorresponds to a case where a signal on a pilot channel transmitted froma given MSC can be received by the mobile terminal 600. Candidate setcorresponds to a case where a signal on a pilot channel transmitted fromthe MSC side is received by the mobile terminal 600 with a sufficientlevel, but the corresponding base station does not belong to Active set.Neighbor set corresponds to a case where it is expected that a basestation will become a candidate, but a signal on a pilot channeltransmitted from the MSC side is received only intermittently.

[0085] Upon reception of the PSMM transmitted from the mobile terminal600, the base station or MSC which manages this base station listupdates the base station list in FIG. 13. More specifically, the basestation or MSC updates the contents of the base station ID written atthe intersection between the terminal ID corresponding to the mobileterminal, which has transmitted the PSMM, and a relationship parameterat each level. In some cases, one base station ID is written at eachintersection, as shown in FIG. 13. In other cases, a plurality of basestation IDs are written at each intersection.

[0086] Here, the following is a description of the processing of S806shown in FIG. 11. That is, in this processing, a radio wave arrivaldirection from a base station other than that is currently engaged incommunications, is estimated. During the estimation, which base stationshould be selected to determine the object of the arrival direction of aplurality of other base station groups, is carried out with use of thebase station list. This processing will now be described with referenceto FIGS. 14 and 15.

[0087] In the check process in S805 shown in FIG. 11, when it isdetermined that a predetermined time period or more has elapsed fromone-previous arrival direction estimation, the terminal transmits acommand for collating the base station list, to the base stationcurrently engaged therewith in communications, or an MSC via this basestation as shown in FIG. 14 (S1201). The base station or MSC which hasreceived the command selects, as a base station to be subjected to thearrival direction, selects:

[0088] (1) at least one of base stations if there are any such stationsother than the station currently engaged with in communications in theActive set of the base station list;

[0089] (2) at least one of stations in cases other than (1), when theCandidate set of the base station list is not empty; or

[0090] (3) if other than (1) or (2), at least one of stations in theNeighbor set of the base station list (S1202). Then, the selected basestation is notified to the mobile terminal 600 (S1203).

[0091] Alternatively, it is possible to consider such a structure asshown in FIG. 15, in which a base station to be subjected to the arrivaldirection is selected from the base station list by a method of theabove (1) to (3) (S1301) after the base station list update processshown in FIG. 12 (S903), and the selected base station is notified tothe mobile terminal 600 (S1302). In this case, unlike the structureshown in FIG. 14, the base station list collation command is not sent toa base station or MSC, and therefore the processing time in S806 can beshortened. On the other hand, with the structure shown in FIG. 14, theselecting operation is conducted only when it is determined that apredetermined time period or more has elapsed from the time of theestimation of the one-previous arrival direction in the judgment processof S805 shown in FIG. 11. Therefore, the overall operation amount can bereduced.

[0092] Further, on the terminal side, it is possible to have such astructure in which the candidate of the base station optimal for thenext handover is selected in advance based on the average height ofelectric field intensity values of several previous times as well as theweakest value, from the monitor result of the pilot channel, and thenthe candidate is selected in S806.

[0093] In addition to the above effect of quickening convergence ofadaptive control on the adaptive array antenna during handover, highlyreliable handover based on a base station list indicating linkassignment priorities can be implemented by the same procedure as thatin the prior art using an omnidirectivity antenna for each mobileterminal.

[0094] Additional advantages and modifications will readily occur tothose skilled in the art. Therefore, the invention in its broaderaspects is not limited to the specific details and representativeembodiments shown and described herein. Accordingly, variousmodifications may be made without departing from the spirit of scope ofthe general inventive concept as defined by the appended claims andtheir equivalents.

What is claimed is:
 1. A mobile communication terminal apparatus whichcommunicates with either a first base station or a second base stationand performs a handover from one to another of the base stations, themobile communication terminal apparatus comprising: an array antennawhich outputs a plurality of signals; a plurality of multipliers thatmultiply the signals output from the array antenna by weighting factors,and output multiplication result signals; a reception device configuredto generate a reception signal based on the multiplication resultsignals output from the multipliers; a control device configured toperform a calculation for the weighting factors based on the receptionsignal, and adaptively control the multipliers by supplying thecalculated weighting factors thereto; and an initial value calculatingdevice configured to calculate at least one initial value for theweighting factors prior to the handover, wherein the control devicestarts the calculation for the weighting factors using the initial valuewhen the handover is performed.
 2. The mobile communication terminalapparatus according to claim 1, wherein the initial value calculatingdevice includes: an estimation device configured to estimate an arrivaldirection of radio waves radiated from the second base station andarrived at the mobile communication terminal apparatus; and a storingdevice configured to store the initial value of the weighting factorsthat is calculated with regard to the arrival direction.
 3. The mobilecommunication terminal apparatus according to claim 1, wherein thereception device performs a radio communication between the mobilecommunication terminal apparatus and the first base station or thesecond base station in accordance with the TDMA(Time Division MultipleAccess) scheme.
 4. The mobile communication terminal apparatus accordingto claim 3, wherein the estimation device estimates said arrivaldirection through a time zone other than a time slot specified in theTDMA scheme.
 5. The mobile communication terminal apparatus according toclaim 1, wherein the reception device performs a radio communicationbetween the mobile communication terminal apparatus and the first basestation or the second base station in accordance with the CDMA(CodeDivision Multiple Access) scheme.
 6. The mobile communication terminalapparatus according to claim 2, wherein the estimation device acquires abase station list from the first base station or other base stations,and selects the second base station among the other base stations withreference to the base station list.
 7. The mobile communication terminalapparatus according to claim 1, wherein the initial value calculatingdevice updates the initial value for the weighting factors calculatedwith regard to the arrival direction by applying an adaptive controlalgorithm including LMS(Least Mean Square) to the initial value.
 8. Themobile communication terminal apparatus according to claim 1, whereinthe initial value calculating device outputs the initial value for theweighting factors calculated with regard to the arrival direction when areception level is higher than a predetermined threshold value.
 9. Amobile communication terminal apparatus which communicates with either afirst base station or a second base station and performs a handover fromone to another of the base stations, the mobile communication terminalapparatus comprising: an array antenna which outputs a plurality ofsignals; a plurality of multipliers that multiply the signals outputfrom the array antenna by weighting factors, and output multiplicationresult signals; a reception device configured to generate a receptionsignal based on the multiplication result signals output from themultipliers; a control device configured to perform a calculation forthe weighting factors based on the reception signal, and adaptivelycontrol the multipliers by supplying the calculated weighting factorsthereto; an initial value calculating device configured to calculate atleast one initial value for the weighting factors prior to the handover,the initial value calculating device including: an estimation deviceconfigured to estimate an arrival direction of radio waves radiated fromthe second base station and arrived at the mobile communication terminalapparatus; and a storing device configured to store information thatidentifies the estimated arrival direction; wherein the control devicestarts the calculation for the weighting factors using the initial valuewhen the handover is performed.
 10. The mobile communication terminalapparatus according to claim 9, wherein the reception device performs aradio communication between the mobile communication terminal apparatusand the first base station or the second base station in accordance withthe TDMA(Time Division Multiple Access) scheme.
 11. The mobilecommunication terminal apparatus according to claim 10, wherein theestimation device estimates said arrival direction through a time zoneother than a time slot specified in the TDMA scheme.
 12. The mobilecommunication terminal apparatus according to claim 9, wherein thereception device performs a radio communication between the mobilecommunication terminal apparatus and the first base station or thesecond base station in accordance with the CDMA(Code Division MultipleAccess) scheme.
 13. The mobile communication terminal apparatusaccording to claim 12, wherein the estimation device acquires a basestation list from the first base station or other base stations, andselects the second base station among the other base stations withreference to the base station list.
 14. The mobile communicationterminal apparatus according to claim 9, wherein the initial valuecalculating device updates the initial value for the weighting factorscalculated with regard to the arrival direction by applying an adaptivecontrol algorithm including LMS(Least Mean Square) to the initial value.15. The mobile communication terminal apparatus according to claim 9,wherein the initial value calculating device outputs the initial valuefor the weighting factors calculated with regard to the arrivaldirection when a reception level is higher than a predeterminedthreshold value.
 16. A mobile communication terminal apparatus whichcommunicates with either a first base station or a second base stationand performs a handover from one to another of the base stations, themobile communication terminal apparatus comprising: an array antennawhich outputs a plurality of signals; a plurality of multipliers thatmultiply the signals output from the array antenna by weighting factors,and output multiplication result signals; a reception device configuredto generate a reception signal based on the multiplication resultsignals output from the multipliers; a control device configured toperform a calculation for the weighting factors based on the receptionsignal, and adaptively control the multipliers by supplying thecalculated weighting factors thereto; an initial value calculatingdevice configured to calculate at least one initial value for theweighting factors prior to the handover; a storing device configured tostore the calculated initial value; wherein the control device startsthe calculation for the weighting factors using the initial value whenthe handover is performed.
 17. The mobile communication terminalapparatus according to claim 16, wherein the reception device performs aradio communication between the mobile communication terminal apparatusand the first base station or the second base station in accordance withthe TDMA(Time Division Multiple Access) scheme.
 18. The mobilecommunication terminal apparatus according to claim 16, wherein thereception device performs a radio communication between the mobilecommunication terminal apparatus and the first base station or thesecond base station in accordance with the CDMA(Code Division MultipleAccess) scheme.
 19. The mobile communication terminal apparatusaccording to claim 1, further comprising: a first synchronizationcircuit for bit synchronization and frame synchronization, which is usedfor communication with the first base station; and a secondsynchronization circuit for bit synchronization and framesynchronization, which is used for communication with the second basestation.